First use system-config-display to set the Montor (Virtual Box output) to 1920x1200. ​ Then reboot, then re-install VBOX Guest Additions and reboot once more. Once the machine comes back and you have logged in, you may need to resize/​maximize the current window to get the desktop to stretch properly.

First use system-config-display to set the Montor (Virtual Box output) to 1920x1200. ​ Then reboot, then re-install VBOX Guest Additions and reboot once more. Once the machine comes back and you have logged in, you may need to resize/​maximize the current window to get the desktop to stretch properly.